1. Field
The embodiments described below relate generally to imaging, and more particularly to the generation of tomographic images.
2. Description
Three-dimensional imaging systems are commonly used to generate images of an internal portion of a body. In one example, a computed tomography (CT) system includes an X-ray source and a radiation receiver that are mounted to face one another on opposite sides of a ring. A body is positioned within the ring so that a portion of interest lies between the X-ray source and the radiation receiver. The X-ray source then emits X-ray radiation that passes through the portion of interest and is received by the radiation receiver.
The receiver produces a set of data that represents the attenuative properties of tissues that lie between the X-ray source and the receiver. This set of data comprises a projection image. The ring is then rotated in order to rotate the X-ray source and the radiation receiver around the portion of interest. During the rotation, the X-ray source transmits radiation toward the receiver and the receiver produces projection images corresponding to various rotational angle positions. A three-dimensional image of the portion of interest may be generated from the projection images using known reconstruction techniques.
The three-dimensional image may be used to diagnose illness, to plan radiation therapy, to confirm patient positioning prior to therapy, and/or to perform image-guided radiotherapy (IGRT). IGRT, for example, requires frequent (e.g., daily) imaging in order to reduce treatment margin and increase target dose accumulation.
Healthy tissue is exposed to radiation during imaging as described above. For example, treatment of breast tissue using IGRT exposes the non-cancerous breast to non-trivial amounts of radiation. It is feared that such radiation may result in future cancer of the non-cancerous breast.
Techniques are desired to provide adequate imaging of a volume of interest while reducing a dose absorbed by other patient volumes.